Optical wireless communication systems offer a number of advantages over their radio frequency counterparts. The advantages include freedom from fading, freedom from spectrum regulations and abundant bandwidth. The main limitations of optical wireless systems include background noise attributed to natural and artificial light sources and multipath propagation. The former degrades the signal to noise ratio while the latter limits the maximum achievable data rate. This thesis investigates the use of transmit power adaptation in the design of optical wireless spot-diffusing systems to increase the power associated with the main impulse response components, resulting in a compact impulse response and a system that is able to achieve higher data rates. The work also investigates the use of imaging diversity receivers that can reject the background noise components received in directions not associated with the signal. The two techniques help improve the optical wireless system performance. The multibeam transmitter and the multi-detector angle diversity receiver or imaging receiver form a multiple input multiple output (MIMO) system. The work also investigates additional methods that can improve the performance such as transmitter beam angle adaptation, and improved modulation and coding in the form of multi-carrier code division multiple access (MC-CDMA). Furthermore, the work investigates the robustness of a link design that adopts the combination of these methods in a realistic environment with full mobility.